1. Technical Field
The present invention relates to a surface emitting laser apparatus.
2. Related Art
FIG. 5 is a block diagram of a conventional surface emitting laser apparatus used in various applications such as an optical interconnection. As shown in FIG. 5, a surface emitting laser apparatus 400 includes an arithmetic processing unit 401, a surface emitting laser device 402, and a laser driving unit 403 connected between the arithmetic processing unit 401 and the surface emitting laser device 402.
The arithmetic processing unit 401 performs calculations according to instructions form the outside, and outputs a differential voltage signal Vs401 based on the calculation results. The arithmetic processing unit 401 receives supply voltages V401 and V402 from the outside. The supply voltage V401 is an I/O voltage of 3.3 V, and the supply voltage V402 is a core voltage of 1.5 V, for example. The laser driving unit 403 amplifies the differential voltage Vs401 from the arithmetic processing unit 401, superimposes a bias voltage Vb401 on the amplified voltage, and outputs the result as a drive voltage signal Vd401. The surface emitting laser device 402 receives the drive voltage signal Vd401 from the laser driving unit 403, and outputs laser signal light of a predetermined wavelength. The laser light output from the surface emitting laser device 402 has a wavelength corresponding to the energy bandgap of the semiconductor material of the active layer. The bias voltage Vb401 supplied to the surface emitting laser device 402 also corresponds to the energy bandgap of the semiconductor material of the active layer. For example, if the oscillation wavelength of the surface emitting laser device 402 is in the 850-nm band, the bias voltage Vb401 of approximately 3.3 V is usually supplied.
Lower power consumption is desired for surface emitting laser devices used in many ways, not only for surface emitting laser devices used for optical interconnection. One method being studied for decreasing the power consumption involves using a surface emitting laser device with a wavelength no less than 1000 nm that can significantly lower the bias voltage and the energy bandgap of the active layer, as shown in Nonpatent Document 1, for example.
Nonpatent Document 1: N. Suzuki, et al., “25-Gbps operation of 1.1-μm-range InGaAs VCSELs for high-speed optical interconnections”, OFA4, OFC2006
The conventional surface emitting laser apparatus, however, cannot achieve sufficient reduction in power consumption by decreasing the power consumption of the surface emitting laser device. For example, in the surface emitting laser apparatus 400 shown FIG. 5, even if the bias voltage supplied to the surface emitting laser device 402 were lowered to 1.5 V, for example, the bias voltage Vb401, which is generally approximately 3.3 V, is supplied to the laser driving unit 403. Therefore, the bias voltage Vb401 must be stepped down by the laser driving unit 403 and then supplied to the surface emitting laser device 402. As a result, the laser driving unit 403 consumes an excessive amount of power for the voltage step-down. Furthermore, the laser driving unit 403 generally uses power to amplify a modulation signal of the differential voltage Vs401 output from the arithmetic processing unit 401 from ±100 mV to ±200 mV, for example. As a result, even when the power consumption of the surface emitting laser device 402 is lowered to 100 mW, for example, the power consumption of the laser driving unit 403 is as high as 500 mW to 1 W. Therefore, the surface emitting laser apparatus 400 cannot achieve sufficient reduction of power consumption in total.